i just finished my gcses this year and I didn't really revise until the last year or a few months before that but it is always good to start revising subjects early. first I would say to just know what exam boards you are doing and if you can buy revision books or flashcards. my favourite books have always been CGP.
maths- Corbett maths has revision videos and questions, maths genie, first class maths, Cognito are also good websites for revision videos. maths genie also has a section for past papers
triple science- free science lessons, cognito, primrose kitten, scienceshorts and dr de bruin all have good revision videos. for past papers, revision science is the best place to go. also physics and maths tutor have flashcards, mindmaps and practice questions. studymind is also a good website too
french- listening to french music and watching french films is supposed to help with the listening part of the course. for reading, it is mostly about learning how to pick out key words from the text. writing mostly gets better with practice and also knowing your tenses very well
business- for business i would mostly recommend just learning the exam technique and how to tackle the questions. also flashcards are good for revising the content and learning calculations
in general, i would say seneca is good for a brief overview and quizlet is a good way to make flashcards online or you can use gizmo which is a website that generates flashcards. there is also the normal websites like bitesize or savemyexams. as you still have 2 years left, i wouldn't overly revise unless you want to get a head start depending on what grades you are aiming for